Willwood Formation facts for kids
Quick facts for kids Willwood FormationStratigraphic range: Thanetian-Ypresian (Clarkforkian-Bridgerian) ~56–48Ma |
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|---|---|
| Type | Geological formation |
| Sub-units | Gray Bull beds, Sand Coulee beds, Sand Creek Facies, Wa-1 Zone |
| Lithology | |
| Primary | Mudstone, shale |
| Other | Sandstone, conglomerate |
| Location | |
| Coordinates | 44°30′N 108°00′W / 44.5°N 108.0°W |
| Approximate paleocoordinates | 49°12′N 90°48′W / 49.2°N 90.8°W |
| Region |  Wyoming |
| Country |  USA |
| Extent | Bighorn Basin |
| Type section | |
| Named for | Shale, mudstone, limestone |
The Willwood Formation is a special layer of rock that tells us about Earth's past. It was formed a very long time ago, between about 56 and 48 million years ago. This time period is known as the late Paleocene and early Eocene epochs. Scientists use different names for these time periods based on the types of mammals found, like Clarkforkian, Wasatchian, and Bridgerian.
Contents
What is the Willwood Formation?
The Willwood Formation is made up of different kinds of sedimentary rocks. These are rocks formed from bits of older rocks, sand, and mud that settled down over time.
Types of Rocks Found
- It mostly has fine-grained rocks like mudstone and shale. These are made from very tiny particles, like mud.
- Mixed in with these are medium-grained rocks called sandstone, which are made from sand.
- You can also find some conglomerate rocks. These are like natural concrete, made of larger, rounded pebbles and rocks stuck together.
Where Can You Find It?
This rock formation is found in parts of the Bighorn Basin in Wyoming, USA. This area includes several counties: Big Horn, Hot Springs, Park, and Washakie.
How Old is the Willwood Formation?
Scientists can figure out the age of these rocks using special methods.
- One way is called radiometric dating. This involves looking at tiny amounts of volcanic ash (called tuffs) found in the rocks. By measuring certain elements in the ash, scientists can tell how old it is.
- Another method is magnetostratigraphy. This looks at the Earth's magnetic field, which has flipped many times throughout history. These flips leave a record in the rocks.
- By using these methods, scientists have found that the Willwood Formation is about 55 to 52 million years old. This means that the important boundary between the Paleocene and Eocene epochs is found close to the bottom of this rock layer.
Ancient Life in the Willwood Formation
The Willwood Formation is famous for the amazing fossils it contains. These fossils give us clues about the animals and plants that lived millions of years ago.
Fossil Animals Discovered
Scientists have found many different types of fossils here:
- Trace fossils: These are not parts of animals themselves, but signs of their activity, like footprints or burrows.
- Birds: Some ancient birds found include Gastornis, which was a very large, flightless bird, and Neocathartes and Paracathartes, which were ancient relatives of vultures.
- Alligators: A fossil of an ancient alligator-like creature called Orthogenysuchus was also discovered in these rocks.
